Sedney started athletics at the age of five at ARV Ilion in Zoetermeer. Until she was 14, she combined athletics with hockey at hockey club MHCZ in Zoetermeer. At the age of 15, Sedney decided to focus solely on athletics, a decision that paid off with qualifications in four individual events (100m, 200m, 400m and 100m hurdles) at the European Youth Olympic Festival in Győr, Hungary in 2017. Sedney eventually competed in the 200m and 100m hurdles, winning gold in both events. At the same competition she was also part of the Dutch Relay Team (Sedney, Minke Bisschops, Suzanne Libbers and Anna Roelofs), which won a silver medal in the 4 x 100 meter relay.